The capture of images of a given object using penetrating energy (such as X-rays or the like) is well known in the art. Such images often comprise areas that are relatively darker or lighter (or which otherwise contrast with respect to one another) as a function of the density, path length, and composition of the constituent materials that comprise the object being imaged. This, in turn, can serve to provide views of objects that are otherwise occluded from visual inspection.
The use of penetrating images finds myriad applications. In at least some application settings, however, merely ascertaining the shape of an occluded object may be insufficient to address all attendant needs. In a security application setting, for example, objects that pose a serious security concern may share a same shape with other completely innocuous objects. In cases where the densities of such objects are similar, it can become impossible to discern from such data which constitutes a threat and which does not. A similar problem can occur when the density and path length product for two objects is substantially the same notwithstanding that they are formed of different materials. As a simple illustration in this regard, a four inch by four inch by three inch block of steel may look the same using two-dimensional radiography as a four inch by four inch by 1.75 inch block of lead notwithstanding that these two materials have considerably different densities.
This, in turn, can greatly increase the unreliability of a security screening process that relies upon such data and/or can greatly increase the amount of extra time that must be committed to following up with each such ambiguous image interpretation. In either case, these existing processes are heavily dependent upon human interpretation and hence are labor intensive and heavily prone to error due to human frailties of one kind or another.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.